1. Field of the Invention
The present invention relates to a method of manufacturing a very small and thin planar inductance element.
2. Description of the Related Art
In recent years, miniaturization of various electronic equipments has been proceeding. Accordingly, a volume ratio of a power supply to the entire electronic equipment tends to increase because of the following reason. That is, although various circuits have been integrated as an LSI, miniaturization and lightening of inductance elements such as an inductor and a transformer which are indespensable circuit elements for a power supply have not been realized.
Therefore, various attempts have been performed to make inductance elements planar to miniatualize them. For example, a planar inductor having the following structure is known. That is, a spiral planar coil is patterned by wet etching a conductive film formed on an insulating substrate such as a polyimide film, an insulating layer is placed on a spiral planar coil, and both the surfaces of the resultant structure are sandwiched by magnetic members such as ferrite plates and amorphous alloy foils. Similarly, a transformer having the following structure is known. That is, a primary and a secondary spiral coils are formed through an insulating layer, both the surfaces of the resultant structure are sandwiched by insulating layers, and magnetic members are formed on the insulating layers, respectively.
In addition, there is an attempt to manufacture a planar inductance element using only the same thin film process as that used in the manufacture of a semiconductor device. For example, a planar inductor is manufactured as follows. An underlying insulating film, a magnetic film, and an insulating interlayer are sequentially formed on the surface of an Si substrate. A conductive film is formed on the insulating interlayer, and then planar coils are formed by photolithography. An insulating film for burying between the lines of the planar coils and covering the upper surface thereof is formed, and a magnetic film is formed thereon. Further, the magnetic film is processed and then is annealed in a magnetic field, and the characteristics of the resultant elements are evaluated. Thereafter, the resultant elements are diced.
Also, a planar transformer is manufactured as follows. That is, an underlying insulating film, a magnetic film, and an insulating interlayer are sequentially formed on the surface of an Si substrate. A conductive film is formed on the insulating interlayer, primary planar coils are formed by photolithography. An insulating interlayer for burying between the lines of the primary planar coils and covering the upper surface thereof is formed. A conductive film is formed on the insulating interlayer, and the secondary planar coils are formed by photolithography. An insulating interlayer for burying between the lines of the secondary planar coils and covering the upper surface thereof is formed, and a magnetic film is formed thereon. Further, the magnetic film is processed and then is annealed in a magnetic field, and the characteristics of the resultant elements are evaluated. Thereafter, the resultant elements are diced.
However, since the conventional methods have the following many drawbacks, planar inductance elements are not practically manufactured.
First, in the manufacture of a planar inductance element using a thin film process, a technique of regulating a stress generated by thermal hysteresis caused by stacking thin films, and a technique of burying an insulator to secure the insulation between the lines of coils cannot be established. For this reason, the yield of manufactured inductance elements is decreased, thereby increasing the production cost. In addition, since a stress remains in the inductance element manufactured by the method described above, magnetic anisotropic dispersion occurs due to a so-called reverse magnetostrictive effect. As a result, a high-frequency loss is increased, the quality coefficient Q as an inductance element is decreased, and the planar inductance element cannot be practically used.
Second, in a planar inductance element formed by a method using a planar coil formed by patterning a conductive film on an insulating substrate such as a polyimide film, and magnetic films such as amorphous alloy foils and ferrite plates, a decrease in thickness and miniaturization of the inductance element are limited, and intervals between the lines of a coil cannot be decreased. For this reason, the inductance is decreased, and the quality coefficient Q is undesirably decreased.
As described above, planar inductance elements manufactured by the above conventional methods cannot realize an excellent frequency characteristic necessary for miniaturization of inductance element.